The present invention relates to transmissions, and more particularly to dual clutch transmissions.
Dual clutch transmissions (DCTs) are well known and include two clutches arranged so that the transmission can transfer drive from one gear ratio to another without interrupting the torque transmitted to the output drive. A typical dual clutch transmission uses two separate clutches and two separate input shafts for odd and even gear sets or gears connected to the inner input shaft and those connected to the outer input shaft. This allows an odd gear set to be “pre-selected” while an even gear set is in use, or an even gear set to be pre-selected while an odd gear set is in use or transmitting torque to the ground. When it is time to shift to the pre-selected gear any time after the torque and speed have been transferred to the opposite clutch, the engaged clutch can be disengaged, and the disengaged clutch can be engaged, thereby shifting without torque interrupt. The clutch “handover” of a conventional DCT provides a smooth transition between sequential gears without loss of power.
DCTs have provided a number of improvements over conventional manual and automatic transmissions. For example, use of a multiple-plate clutch assembly avoids inefficiencies associated with torque converters commonly found in automatic transmissions. DCTs are typically lighter than comparable automatic transmissions, and can provide improved fuel economy and quicker shift periods than a comparable manual transmission. Although DCTs provide a marked improvement in many respects over other types of transmission, DCTs can be difficult to implement and to package within the tight space constraints associated with today's vehicle design. This is particularly true in applications where a larger number of transmission speeds are desired.
Synchronizers are also well known and are included on many DCTs and in a variety of configurations. For example, some synchronizers are configured to engage only a single gear (i.e., a half synchronizer) and have one neutral position and one engaged position. Other synchronizers are configured to engage one of two gears (i.e., a dual synchronizer) and have one neutral position and two engaged positions. In some transmission configurations it can be desirable to simultaneously engage two gears. In these configurations, two half synchronizers are generally positioned back to back along the same shaft, each being controlled by a separate shift fork. The inclusion of two synchronizers adds bulk to the overall transmission assembly, however, and can be difficult to implement in DCTs and in single clutch transmissions.